The invention is directed to a method for the local removal of insulating layers on a semiconductor substrate in a vacuum chamber with the assistance of laser light.
It is frequently necessary in semiconductor technology to undertake microwork at a semiconductor substrate during the manufacture of integrated circuits on the semiconductor substrate. Included are the local removal of passivation or insulating layers in circuits metallized in single-layer or multi-layer fashion, with the object of making conductive structures such as, for example, interconnects or pads accessible for various purposes. For example, analyses or electrical measuring and testing are such purposes. Furthermore, the locally exposed interconnects can be electrically conductively connected to one another by metal deposition in order to be able to simply implement potential design modifications and to check their compatibility. Semiconductor modules can also be repaired in the same way.
When the insulating layer to be removed is composed of silicon nitride or of an organic material such as, for example, polyimide, then it can be locally removed with the assistance of a pulsed UV laser on the basis of what is referred to as ablation in that the laser beam is directed or focused onto the desired location. Such an ablation, however, is not possible given an insulating layer having a high UV transmission such as, for example, silicon oxide and other glass-like layers since the layer lying therebelow would be damaged by the intense UV radiation. A number of laser-induced etching processes are known for the local removal of silicon oxide layers and are described in the article by G. Loper and M. Tabat in SPIE Vol. 459, Laser Assisted Deposition Etching and Doping (1984), pages 121-127, incorporated herein. Such laser-induced etching processes are based on the defined generation of highly reactive radicals from halogen-carbon compounds with the assistance of pulsed UV lasers in a vacuum chamber, so that a chemical reaction of the silicon oxide with these radicals occurs upon formation of volatile silicon and oxygen compounds. The gaseous chlorine and fluorine compounds utilized, however, have high toxicity and have an extreme corrosive effect on many materials, so that a high technological expenditure is required. Mechanical parts situated in the vacuum chamber such as, for example, xyz-tables for exact positioning of the semiconductor substrate to be processed become unusable within a short time due to the corrosion.